In optical data storage, micron size and larger bits, spots or other marks representing data bits are melted, oblated, embossed or otherwise marked on the surface of an optical data storage medium. The data may then be read with a photodiode detector or linear CCD array which images data spots illuminated by a laser or light emitting diode (LED) light beam or other illuminating source. Usually either the emitting beam or the data storage medium is moved relative to the other so that the data may be scanned.
For data recordings which are linked and yet distinct, separate recordings may be disposed upon a data field of a medium with each recording contained within a data page. For example, a data page may have dimensions of 1 mm.times.1 mm, with 100 rows having as many as 100 data bits in each row. The data bits are contained within data cells in the order of 1 micron up to 100 microns with 10 microns being a preferred size. Thus, more than 2000 data pages may be arranged in rows and columns on a surface the size of a credit card. U.S. Pat. No. 3,806,643 to Russell teaches a method for reading data pages. A single row of microlenses is positioned behind a data field in a laser beam and scanned horizontally to illuminate the first line of each data page across the data field. This illumination of a line is transmitted to the row of microlenses whereafter the data field is caused to be moved vertically for reading of a second line of the data pages. The lines of the illuminated pages are transmitted seriatim to the row of microlenses. Because of the size of the data bits involved, it is imperative that any skew of the microlenses relative to the data field be kept within extremely tight tolerances.
The charge-coupled device (CCD) is a device which was originally developed for military use but has become increasingly popular for scientific applications. The CCD is the functional equivalent of electronic film. The CCD is made up of an array of detector cells, also known as pixels or picture elements. When exposed to light, electrons accumulate at each pixel as electron-hole pairs are generated within the CCD. The generation of electron-hole pairs is in direct proportion to the intensity of the light received. Electrons which are accumulated in the various pixels are then transferred out in a process referred to as "charge-coupling".
The problem with use of a CCD is that imaging of data must be both photometrically and geometrically extremely accurate. For example, a CCD area array of 360,000 picture elements disposed in 600 rows of 600 picture elements each must not be skewed relative to the surface to be read. In reading a data page, such a CCD area array could read an entire data page but imaging of the data page would require that the peripheral edges of the CCD area array be kept parallel the peripheral edges of the data page. The prior art insures proper alignment by keeping the manufacture of the data field to be read and the equipment for reading the data field within extremely tight tolerances. This degree of precision is not practical when dealing with data bits in the range of 1 to 10 microns.
It is an object of the present invention to devise a method and apparatus for reading a data surface in a manner which insures proper orientation of CCD imaging.